1. Field of the Invention
The present invention relates to a filler for a sliding gate, in particular, a filler for a sliding gate which is not melted, sintered or penetrated by molten metal (molten steel) poured into a ladle in a steel works and therefore is easily discharged to let the molten metal through the gate.
2. Description of Related Art
A ladle receiving molten steel in a steel works is provided with a sliding gate. The ladle with the sliding gate is required to be fed with a filler comprising refractory powder before molten steel is introduced into the ladle, for the purpose of preventing the molten steel from solidifying in the gate.
Conventional fillers, however, sometimes form a sintered layer due to molten steel and block the opening of the gate. Since such blocking prevents the molten steel poured in the ladle from being discharged, workers often have to, for example, pound the filler block with iron rods. Such a work is extremely dangerous and, in view of inhibiting labor accidents, it is highly demanded that the possibility that the blocking does not occur (hereafter referred to as non-blocking ratio) should be brought close to 100%.
In addition, in today's prevailing manufacture facilities for continuous casting, the blocking generated in gates cause a lot of problems in operation. In some cases, after being primarily smelted in a converter, steel is secondarily smelted for deoxygenation, dephosphorization or desulfurization in a ladle for a long time. Certain kinds of steel are held in the ladle in a molten state for as long as about 7 to 8 hours. Therefore, there is demand for a filler for sliding gates capable of withstanding such conditions.
As a filler, silica sand is conventionally used. However, in view of resistance to fire, sand obtained by subjecting refractory natural chrome ore to drying and classification (hereafter referred to as chromite sand) is sometimes used as a filler.
Since the chromite sand tends to sinter and cause the blocking at the casting of molten steel, however, the chromite sand is rarely used independently as a filler. In general, as described in Japanese Patent Publication No. Sho 60(1985)-57942, the chromite sand is disposed to form a lower layer in a sliding gate and the silica sand is disposed to form an upper layer therein.
However, when the silica sand and chromite sand are used in complete separation as described in the above Patent Publication, they sometimes cause the blocking in the sliding gate, which leads to an unsatisfactory non-blocking ratio.